Diagnosing a confusing switch matrix issue.
On a TZ, the U20 chip (2803) will blow after a few plays.
Hence, with all connectors plugged in, we are finding some overvoltage on a few of the rows (white wires). But none of the columns (green wires)
Most lines, such as the green wire connectors, are at approx 11.5volts but a few of the white wire leads for rows, are as high as 13.9volts
So unpluging a number of connectors to find which ones allow the voltage to drop has narrowed it down to the OPTO switch circuits being suspect.
(Note that NO change observed for disconnecting Lamp, Coil or Flasher circuits.
and all underplayfield micro and leaf switches inspected for shorts.
Also, as information, CPU, Power Driver and 10-opto boards have been serviced.)
So, overvoltage is the problem.
General Question: Is a reading of 12.5volts tolerable?
Apparently so, as I measure some voltages on a STTNG, at least one of the circuits is at 12.6volts.
Can anyone confirm for sure considering the general "plus or minus 10% tolerance" principle for components?
Next, disconnecting all the opto sensors connectors under the playfield, I see a drop to the 12.5volt level and then reconnecting certain ones (2 or 3) will then increase back to 13.5+volts.
Question: So what about the simple Opto sensors could raise the voltage? Only a short or some other failing of components? (Apparently this game took hit during a lightning storm)
No voltage change when plugging the clock opto connector but the Power miniplayfield is one that boosts the voltage back up. I have yet to check for pinched wires, etc under that playfield.
Any helpful thoughts would be most appreciated. Other questions to clarify are welcome to help all learn from the discussion. Thanks.